A technique has been known in which the crystals of the channel region of a semiconductor device including a field-effect transistor are distorted to increase the carrier mobility. For example, a method has been proposed for forming a stress film covering the field-effect transistor so that a predetermined stress may be produced in the channel region.
The field-effect transistor has a structure having side walls that electrically separate the gate electrode from the source and drain regions when the gate electrode, the source region and the drain region are formed. The side walls are formed on the side surfaces of the gate electrode and at both ends of the channel region.
A side wall having a small width may increase the stress produced in the channel region by the stress film, and may increase the carrier mobility accordingly. However, the side wall having a small width may not maintain sufficient insulation between the gate electrode and the source region or between the gate electrode and the drain region.
For example, Japanese Laid-open Patent Publication No. 2005-057301 discusses that grooves are formed so as to extend to the portions under the side walls from the surfaces of the source and drain regions formed at both sides of the side walls, and are filled with a stress film. By forming grooves near the channel region, the distance between the stress film and the channel region may be reduced independent of the width of the side wall.